What are six key traits that define life?
- High chemical and structural complexity, 2. Ability to extract, transform, and use energy, 3. Defined functions and regulated interactions, 4. Ability to sense and respond to environment, 5. Capacity to self-replicate, 6. Capacity to evolve
Why does life require a continual input of energy?
Without energy input, molecules decay toward disorder and equilibrium with the environment; energy keeps life organized.
Why do cells need a plasma membrane?
It acts as a selective barrier, allows nutrient import and waste export, and maintains a distinct intracellular environment.
What roles do proteins play in cells?
Structural support, movement, signal detection, catalysis (enzymes), and other specific functions.
How is DNA chemically different from proteins?
DNA has 4 nucleotides; proteins have 20 amino acids. DNA is simpler chemically.
What is the central dogma of molecular biology?
DNA → RNA → Protein (information flows from DNA to RNA to protein).
What is transcription?
The process of copying information from DNA into RNA (mRNA).
What is translation?
The process of synthesizing proteins from mRNA using ribosomes.
How does the genetic code work?
RNA is read in triplets (codons), each specifying one of 20 amino acids; 4 nucleotides form 64 possible codons.
What is the role of tRNA in translation?
tRNA carries specific amino acids and matches its anticodon to the mRNA codon to add the correct amino acid.
What is the role of rRNA in ribosomes?
rRNA, along with proteins, forms ribosomes and catalyzes protein synthesis.
Can proteins be converted back into RNA or DNA?
Generally no; the information flow is unidirectional (DNA → RNA → Protein).
Why is the universality of DNA important?
It allows us to study shared ancestry, estimate evolutionary timelines, and understand early life events.
Why are cells considered open systems?
They require continuous import of energy and materials and export waste to maintain life functions.
How do membranes help cells remain out of equilibrium?
By controlling what enters and leaves the cell, they maintain concentrations of nutrients and molecules different from the surroundings.
How does life maintain order despite the natural tendency of molecules toward disorder?
Life uses a continual input of energy to maintain complex structures and prevent decay toward equilibrium.
Why is the plasma membrane crucial for a cell’s energy management?
By selectively importing nutrients and exporting waste, the membrane allows the cell to accumulate energy sources and maintain a distinct internal environment.
How do proteins enable a cell to respond to its environment?
Proteins can sense signals, detect changes, and catalyze reactions, allowing the cell to adjust its behavior and metabolism.
Why is DNA simpler than proteins but sufficient for genetic information?
DNA has only 4 nucleotides, but the linear sequences and pairing rules allow it to encode vast amounts of information, which proteins can then implement.
How does the central dogma connect genetic information to cellular function?
DNA stores the information, RNA transcribes it, and proteins carry out functions. This flow ensures that genes control cell behavior through functional molecules.
How does reading RNA in triplets (codons) allow for more information to be stored?
Three nucleotides per codon create 64 combinations, enough to specify all 20 amino acids and provide redundancy to prevent translation errors.
How do tRNA and ribosomes work together to synthesize proteins?
tRNA carries amino acids matching mRNA codons, while ribosomes catalyze peptide bonds, linking amino acids into proteins according to the genetic code.
How does the universality of DNA support evolutionary studies?
Since all life shares the same molecular principles, comparing DNA sequences reveals common ancestry, evolutionary events, and timelines of life’s history.
Why can’t proteins generally be used to recreate RNA or DNA?
Proteins lack the information storage format and nucleotide sequence needed to reconstruct nucleic acids, enforcing unidirectional information flow.
